Rubber compositions including natural rubber are widely used in industrial products such as pneumatic tires, belts, and adhesives since the mechanical properties thereof are excellent. However, in addition to excellent mechanical properties, improving fuel efficiency by reducing hysteresis loss and improving molding processibility by reducing viscosity are desired for tread rubber of pneumatic tires. However, these properties are not necessarily sufficient with conventional rubber compositions containing natural rubber.
Also, epoxidation of natural rubber, graft polymerization of organic compounds, deproteinating treatments, and the like are known as modification means for imbuing natural rubber with new properties. For example, Japanese Patent Application Publication No. 2002-201203 suggests cross-linking proteins in a natural rubber latex by adding a protein denaturing agent such as glutaraldehyde thereto.
However, it was not possible to achieve the performance required for improvement in molding processibility by low viscosity or for reduction of hysteresis loss even for a rubber composition including modified natural rubber obtained by such modification means.
An object of the present invention is to provide a method for producing a rubber composition that reduces viscosity and improves molding processibility of a rubber composition with natural rubber, as well as reduces hysteresis loss.